arTICle | boTulInum ToxIn A |
supercilii(20). The depressor supercilii is a small muscle that has been found to originate directly from bone as one or two distinct muscle heads from the nasal process of the frontal bone and the frontal process of the maxilla, approximately 10 mm above the medial canthal tendon(20). not only does it help move the eyebrow downward and close the eyelid, but the depressor supercilii also participates in the functioning of the physiologic lacrimal pump by compressing the lacrimal sac. opening and closing the eyelids is partially
accomplished by the contraction of the accessory muscles of the upper eyelid: one being the levator palpebrae superioris, a striated muscle, the other a non- striated muscle called mueller’s muscle.
occasionally is referred to as the depressor supercilii
by some authors. Contraction of the orbital orbicularis oculi approximates the upper with the lower eyelids, either deliberately or involuntarily. The horizontal lines of the glabella and nasal root are
produced by the contraction of the vertically oriented fibers of the procerus, depressor supercilii and the medial fibers of the orbital orbicularis oculi. These three muscles also are referred to as the medial brow depressors. The procerus is a thin, pyramidal muscle centrally located in the midline between the two eyebrows. It lies 1–4 mm beneath the surface of the skin. The procerus arises from the fascia covering the nasal bridge and lower part of the nasal bone and the upper part of the upper lateral nasal cartilage.
It inserts superiorly into the skin and
subcutaneous tissue at the nasal radix and lower part of the forehead between the two eyebrows. Contraction of the procerus pulls the medial aspect of the eyebrows downward, creating the horizontal frown lines across the root of the nose. Anatomic studies have demonstrated that the procerus can be longer in women than in men (18-19). The depressor supercilii is considered by many a
component part of the medial fibers of the orbital orbicularis oculi (14). Yet others consider it a separate and distinct muscle from the orbicularis oculi and corrugator
38 ❚ March 2011 |
prime-journal.com
Figure 3 The corrugator supercilii lies directly against the bone. (A) Skull with view of the corrugator supercilii superimposed with letters. The thickest part of the belly of the muscle is approximately 2.0 cm from the nasion. (B) A patient with representation of corrugator supercilii drawn in red with superimposed lettering. Abbreviations: X, nasion; O, origin; B, belly; I, insertion of corrugator supercilii
Dilution Different clinicians have their favorite patterns of injecting the glabella with varying doses of different concentrations of onabotulinumtoxinA11. The manufacturer’s package insert recommends reconstituting the 100 u vial of onabotulinumtoxinA with 2.5 ml of unpreserved normal saline. Thus yielding 4 u of onabotulinumtoxinA per 0.1 ml of solution(21). However, since the brow depressors decussate with each other and are in close proximity in a very small and confined area, it is extremely important to inject accurately precise amounts of onabotulinumtoxinA in this area. Therefore, many seasoned injectors still reconstitute the 100 u vial of onabotulinumtoxinA with only 1 ml of normal saline. This provides 1 u of onabotulinumtoxinA in every 0.01 ml of solution which is easily injected using a 0.3ml becton-Dickinson insulin u-100 syringe with a 31 gauge needle directly attached (beckton, Dickinson and Company, 1 becton Drive, Franklin lakes, nJ, uSA 07471). The advantage of using an insulin syringe is that the needle is directly swaged onto the hub of the syringe, so there is little or no additional wastage of product in the hub of the needle or in the neck of the syringe. In addition, each unit line marked on the syringe barrel corresponds to 0.01 ml or 1 u of onabotulinumtoxinA when a 100 u vial of onabotulinumtoxinA is reconstituted with 1 ml of saline. In this way, only minimal volumes of onabotulinumtoxinA will be needed to produce the desired results. In addition, most have now switched to using preserved saline with 0.9% benzyl alcohol (22).
Dosing: how to correct the problem (dos and don’ts) The pre-treatment evaluation should include examining the patient at rest and in full motion. lightly palpate the muscles of the glabellar area with the palmar surface of the finger tips as the person squints and frowns. This will help determine the location, size, and strength of the individual muscles of the glabella. A frequently used and standardized technique for treating the glabella is to inject onabotulinumtoxinA into five different sites with doses that range anywhere from 4–10 or more u at each site(7-13,21). Electromyographic guidance in this area has not particularly improved treatment outcomes because these facial muscles are superficial and easily localized
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